Power factor correction is an important component of increasing efficiency of modern day power delivery systems. Due to reactive components in the loads that consume power such as appliances that include a motor, a phase shift develops between a current and a voltage component of a power signal. The power factor of an AC electric power system is defined as the ratio of the real power flowing to the load to the apparent power and is a number between 0 and 1 (frequently expressed as a percentage, e.g. 0.5 pf=50% pf). Real power (P) is the capacity of the circuit for performing work in a particular time. Apparent power (S) is the product of the current and voltage of the circuit. The Reactive Power (Q) is defined as the square root of the difference of the squares of S and P. Where reactive loads are present, such as with capacitors or inductors, energy storage in the loads result in a time difference between the current and voltage waveforms. During each cycle of the AC voltage, extra energy, in addition to any energy consumed in the load, is temporarily stored in the load in electric or magnetic fields, and then returned to the power grid a fraction of a second later in the cycle. The “ebb and flow” of this nonproductive power increases the current in the line. Thus, a circuit with a low power factor will use higher currents to transfer a given quantity of real power than a circuit with a high power factor. A linear load does not change the shape of the waveform of the current, but may change the relative timing (phase) between voltage and current. Generally, methods and apparatus to correct power factor have involved coupling a fixed corrective load having a known reactive value to a power line. The fixed capacitive reactive load counteracts the reactive effect of inductive loads vice versa, improving the power factor of the line. However, a fixed reactive load is only able to correct the power factor of a power line by a fixed amount to a certain extent because the power factor may be dynamic due to the changing nature of loads that are coupled and decoupled to the power line. To that end, later developments included several fixed reactive loads that may be selectively coupled to a power line in order to correct power factor. However, such systems require monitoring by an operator who must continually monitor the power factor in order to couple and decouple fixed reactive loads in order to counteract the ever changing power factor of the power line.
The changing landscape of electronics has introduced other inefficiencies in the delivery of power. The increased use of personal electrical appliances has caused an increase in the use of wall mounted AC-DC converters to supply power to devices and recharge the batteries of everyday items such as laptops, cellular telephones, cameras, and the like. The ubiquity of such items has caused users to have several of these converters, known as “wall warts” to be coupled into power systems. The two most common AC-DC converters are known as linear converters and switched mode converters. Linear converters utilize a step down transformer to step down the standard 120V power available in US residences to a desired AC voltage. A bridge rectifier rectifies that voltage. The bridge rectifier is generally coupled to a capacitor. Generally, this capacitor is of a high value. The capacitor forms a counter electromotive force. The capacitor forms a near DC voltage as it is charged and discharged. However, as it is charged, the capacitor draws current only a fraction of the cycle by the non linear bridge rectifier. As a result, the current waveform does not match the voltage and contains a heavy harmonic distortion component. Total harmonic distortion (THD) is the sum of the powers of all harmonic components to the power of the fundamental frequency. This harmonic distortion may be reflected back into the power network.
A switching power supply works on a different principle but also injects harmonics into a power delivery network. In general, a switched mode power supply operates by rectifying the 120V voltage available in US residences. The rectification against a counter electro motive force, such as a big reservoir capacitor, again adds harmonics and distortion. Also, the widespread adaptation of various types of linear or switch mode integrated circuits cause the system to create electrical noise. Furthermore, reactive components in the alternating current network degrades power factor, and integrated circuits cause harmonics and noise to be reflected into the power line. These harmonics manifest as harmonic distortion in the current component of a power signal. Because the power network has a nonzero impedance, distortion along the current component may also translate to amplitude distortion. Amplitude distortion is distortion occurring in a system, subsystem, or device when the output amplitude is not a linear function of the input amplitude under specified conditions. Other undesirable effects are also formed, such as power factor distortion and overall reduction of energy transfer. Such effects decrease efficiency and reduce quality in the delivery of power. To that end, what is needed are methods and apparatus capable of not only correcting a power factor in a power delivery network, but also reducing or eliminating distortion in a power line, thereby allowing for maximum efficiency and quality in power delivery. As a result, overall energy consumption may be reduced.